The present invention relates to a line head and an image forming apparatus including the same.
Among image forming apparatuses of the related art, image forming apparatuses in which a laser light source is used as an exposure unit are known.
Among this type of image forming apparatuses, for example, an image forming apparatus (for example, see Japanese Unexamined Patent Application Publication No. 11-198433) in which a line head including electroluminescent elements (hereinafter, referred to as EL elements) as light-emitting elements are used as a light source instead of the laser light source as the exposure unit is known.
Among the line heads, for example, in a line head in which the EL element is of a bottom-emission-type, light emitted from the light-emitting elements is transmitted through a glass layer (an element substrate) where the light-emitting elements are formed, and enters air. However, the traveling direction of the light may be changed or diffused and attenuated in the glass layer due to the total internal reflection caused by a difference in refractive index between the glass layer and air. As a result, the quantity of light which can be transmitted outside from the glass layer may be decreased.
Among the line heads, a technique is also known, in which a micro-lens (or lens) is provided in the substrate which is provided on the light-emitting elements and from which light exits, to efficiently output the emitted light to the outside (for example, see Japanese Unexamined Patent Application Publication No. 2000-77188).
It has therefore been considered to combine the line head composed of the EL elements with the technique which provides the line head with the lenses to provide lenses on the glass layer of the line head, thereby efficiently outputting the light that may be diffused.
However, as described above, for example, even when the line head composed of the EL elements is provided with the lenses, the glass layer (element substrate) is formed with a substantially large thickness in the manufacturing process. Therefore, the light emitted from the light-emitting elements may be absorbed and attenuated while it passes through the glass layer irrespective of the presence of the lenses, which may cause a decrease in efficiency of the light to be output from the glass layer.
Accordingly, it is difficult to efficiently output the light emitted from the light-emitting elements out of the glass layer. This deteriorates the exposure efficiency of the line head.
Also, the provision of the lens portion causes the light emitted from a light-emitting element to enter the lens formed immediately above the adjacent light-emitting layer, thereby generating crosstalk, which deteriorates the exposure efficiency of the line head.
In addition, even in the top-emission-type line head, the same problem occurs in that the sealing substrate is required to be sufficiently thick, similarly to the element substrate.